This invention relates to a method and apparatus for analyzing the surface of a specimen with such as an electron probe microanalyzer (EPMA), a scanning electron microscope (SEM) and the like, and more particularly to background correction of the measured data in such surface microanalyzers.
In an electron microanalyzer or a scanning electron microscope, the surface of a specimen to be analyzed is scanned by an electron beam having a diameter of several tens of angstroms, so that the various kinds of information emerging from each and every minute point on the specimen surface scanned by the electron beam are electrically detected, and displayed in terms of composition of the specimen and/or concentration of the components thereof on a cathode-ray tube in synchronism with the scanning of the specimen surface thereby to display the distribution of the elements contained in the specimen.
Various signals emerge from a specimen surface irradiated by an electron beam. Depending upon which of the signals is used for formation of images, a secondary electron image, a reflected electron image, a luminescence image, a characteristic X-ray image, an Auger electron image, etc. can be observed.
In the above-mentioned surface analysis by means of, for example, characteristic X rays, the peaks of the characteristic X rays emitted by the component elements of the specimen under examination are superimposed on a background caused by the inherent characteristic of the instrument, the conditions of excitation of the specimen and the composition of the specimen. This means that the measured data of the distribution of the elements in the specimen contain errors caused by background. Therefore, it is customary to correct the measured data for the background.
There are known various methods of backgrounds correction. In one of them, a measurement of background is conducted all over the specimen surface before or after scanning the specimen surface, and the measured value is corrected for the background. In another of the known methods, background is measured on some separate points on a specimen surface, and from the measured data the background of the whole specimen surface is surmised thereby to make a background correction of the measured value.
Japanese Unexamined Patent Publication No. 2-10639 discloses a third method of background correction which uses two X-ray spectrometers for each element to be analyzed. The focal points of the two X-ray spectrometers are so set as to coincide on the surface of a specimen to be analyzed, and one of the spectrometers is set to an X-ray wavelength characteristic of an element to be measured contained in the specimen while the other spectrometer is set to a wavelength adjacent to the base of the above-mentioned characteristic X-ray peak wavelength of the element to be measured, and the specimen surface is scanned by both spectrometers simultaneously thereby to obtain both the characteristic X-ray data of the element being measured containing background and the background data at the same time for background correction of the measured data of the specimen.
In the first method, since a measurement of background is conducted all over the surface of a specimen to be analyzed before or after scanning the specimen surface for measurement, the specimen surface is scanned twice, so that a long time is required for analysis of the specimen surface.
In the second method, since background is measured skippingly at several points on the surface of a specimen, the time required for measurement is advantageously shorter than in the first method. Background, however, is caused by not only the characteristic of the instrument and the exciting conditions of the specimen but also the composition of the elements present at the measured spots on the specimen surface, so that accurate background correction cannot be effected.
The third method which uses two X-ray spectrometers for each element to be analyzed has solved the problems involved in the time required for analysis and adverse influences by the elemental composition at the measured spots of the specimen surface. However, two X-ray spectrometers are required for each element to be measured, so that the whole apparatus becomes bulky with an increased manufacturing cost.